Does a Healthy Lifestyle Make You Live Longer or Does It Just Seem Longer?

It's a question I don't think we will ever really know the answer to.  I see people that eat super healthy, exercise regularly and look like they could expire any day now.  Think of a person's immune system as an army of little antibodies ready to attack any threat to your health.  So, it makes sense to me that if you coddle your immune system, it will become weak and not as effective as it could or should be.  Therefore, I believe in throwing everything I can at my immune system to make it strong.  It's like boot camp everyday for your immune system.  As far as exercise, you hear about people all the time that need a knee replaced, torn tendons, etc.  So how does exercise prolong your life?  Parts are parts, and parts wear out.  It's like sitting in you car and revving the engine for thirty minutes and expecting it to prolong the life of you car.  Keep in mind, I'm not a doctor but I could have been if it wasn't for that damn ethics course.  Just some food for thought, or maybe junk food for thought.